The instant invention relates to a brake system that monitors the operation of a drive system which raises and lowers an aircraft passenger loading bridge. In the event of a malfunction of the drive system, the brake system interrupts power to the drive system and actuates a brake to prevent further operation of the drive system.
An aircraft passenger loading bridge provides an enclosed shelter through which passengers can travel between an airport and an aircraft. Normally, one end of the bridge is attached to the terminal and the other end is movable horizontally and vertically to enable it to be precisely aligned with the doorways of different types of aircraft. Typically, a bridge has one drive system which moves the bridge horizontally and another drive system which elevates and lowers the end of the bridge remote from the terminal. In the event of a failure in the system which moves the bridge vertically, it is possible that the bridge could fall rapidly and cause an injury to persons on the bridge. Therefore, it is necessary to have a brake system which will automatically be applied in the event of a failure of the drive system which moves the bridge vertically.
In one aircraft passenger loading bridge manufactured by the assignee of the instant invention, an electric motor drives a pair of ball screws which raise and lower the movable end of the bridge. The motor is connected to the ball screws by a pair of chains. In the event one ball screw becomes inoperative, such as would happen if a chain broke or the ball screw froze, the motor would continue to operate the other ball screw. If the operator continued to actuate the drive system, the operating ball screw would raise one side of the bridge and cause a torsional strain on the bridge which would severely damage it. Accordingly, it is desirable to have a brake system which interrupts the operation of the bridge drive system in the event one ball screw is driving and the other is stationary.
It is also desirable to have a brake system which operates to stop the operation of the bridge in the event both ball screws are operating but one is operating significantly faster or slower than the other.
The primary failure condition which must be protected against by a bridge brake system is that in which the bridge starts to fall too rapidly. In one prior bridge control system, a brake is automatically applied whenever a switch which actuates the vertical bridge drive system is released. A disadvantage of this system is that, if there is a failure of the vertical drive system when an operator is raising or lowering the bridge, the operator must release the switch before the brake can be applied. However, if the operator panics and does not move his hand off of the switch, the brake will not be applied. Therefore, it is desirable to have a bridge brake system which will automatically stop all operation of the bridge drive system as well as apply a brake to stop further vertical movement of the bridge as soon as the rate of movement of the bridge exceeds a predetermined maximum.